Tank

Soldiers from 3rd Armored Cavalry Regiment provide security for other troops with their M1 Abrams main battle tank in Biaj, Iraq

A tank is a tracked armoured fighting vehicle, designed to engage enemy forces by the use of direct fire. A tank is equipped with heavy weapons and armour, as well as by a high degree of mobility that allows it to cross rough terrain at relatively high speeds. While tanks are expensive to operate and logistically demanding, they are among the most formidable and versatile weapons of the modern battlefield, both for their ability to engage other ground targets and their shock value against infantry. While tanks are powerful fighting machines, they seldom operate alone, being organised into armoured units in combined arms forces. Without such support, tanks, despite their armour and mobility, are vulnerable to infantry, mines, artillery, and air power. Tanks are also at a disadvantage in wooded terrain and urban environments, which cancel the advantages of the tank's long-range firepower, limit the crew's ability to detect potential threats, and can even limit the turret's ability to traverse.

Tanks were first used in World War I to break the deadlock of the trenches, and they evolved gradually to assume the role of cavalry on the battlefield. The name tank first arose in British factories making the hulls of the first battle tanks: the workmen were given the impression they were constructing tracked water containers for the British Army, hence keeping the production of a fighting vehicle secret.

During World War I two major types of tanks evolved; the "male tank" which is the vehicle associated with the word today, and the female tank. The female tank contained a series of smaller weapons located around the hull as opposed to the single large weapon seen on today's tanks, and was mainly designed as an anti-infantry platform. After World War I ended this type of vehicle was largely replaced by infantry carriers.

Tanks and armour tactics have undergone many generations of evolution over nearly a century. Although weapons systems and armour continue to be developed, many nations have reconsidered the need for such heavy weaponry in a period characterised by unconventional warfare.

History

World War One: the first tanks

The fighting conditions on the Western Front prompted the British Army to begin research into a self-propelled vehicle which could cross trenches, crush barbed wire, and would be impervious to fire from machine-guns. Having already seen a Rolls-Royce Armoured Car used by Royal Naval Air Service in 1914, and aware of schemes prompted by Major Ernest Swinton to create a tracked fighting vehicle, First Lord of the Admiralty Winston Churchill sponsored the Landships Committee to oversee development of this new weapon. The Landships Committee created the first successful prototype tank, nicknamed Little Willie, which was tested by the British Army in September 1915. Although initially termed landships by the Admiralty, the initial vehicles were colloquially referred to as water carriers, later shortened to tanks, to preserve secrecy. The word tank was used to give the workers the impression they were constructing tracked water containers for the British army in Mesopotamia, and the name became official in December 1915.

The first tank to engage in battle was D1, a Mark I British tank used during the Battle of Flers-Courcellette (part of the Battle of the Somme), near Delville Wood on the 15 September 1916. The tank was commanded by Captain Harold Mortimore and whilst it assisted the British infantry to capture some German trenches, it was knocked out by friendly fire. The French developed the Schneider CA1 working from Holt caterpillar tractors, and first used it on the 16 April 1917. The first successful use of massed tanks in combat meanwhile occurred at the Battle of Cambrai on 20 November 1917. Tanks were also used to great effect in the Battle of Amiens, when Allied forces were able to break through entrenched German position due to armoured support. The tank would eventually make trench warfare obsolete.

Initial results with tanks were mixed; significant reliability problems caused considerable attrition in combat. Deployment in small "penny packets" also lessened their nonetheless formidable tactical value and impact. The spear-thrust type application of the Blitzkrieg was only to be developed fully in WWII.

German forces initially lacked countermeasures, though they did (accidentally) discover solid anti-tank shot, and the use of wider trenches to limit the British tanks' mobility. However, changing battlefield conditions and continued unreliability forced Allied tanks to evolve throughout the war, producing models such as the very long Mark V, which could navigate large obstacles, especially wide trenches, more easily than their predecessors.

Germany fielded a small number of tanks during World War I, notably the A7V, of which only about twenty were produced. The first tank versus tank action took place on 24 April 1918 at Villers-Bretonneux, France, when three British Mark IVs met three German A7Vs.

Demands from infantry to have tanks close by during attacks would have negative effects on British tank design and tactics well into World War II.

Tanks of WWI

Video clip of WWI tanks helping the Allies with an advance in Langres, France (1918).

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Interwar years: advances in design and tactics

Polish Vickers E.

With the tank concept now established, several nations designed and built tanks between the two world wars. The British designs were the most advanced, due largely to their interest in an armoured force during the 1920s. France and Germany did not engage in much development during the early inter War years due to the state of their economy, and the Versailles Treaty respectively. The US did little development during this period because the Cavalry branch was senior to the Armoured branch and managed to absorb most of the funding earmarked for tank development. Even George S. Patton, with tank experience during WWI, transferred from the Armoured branch back to the Cavalry branch during this period (because the US Army decided not to fund a tank corps).

Throughout this period several classes of tanks were common, most of this development taking place in the United Kingdom. Light tanks, typically weighing ten tons or less, were used primarily for scouting and generally mounted a light gun that was useful only against other light tanks. The medium tanks, or cruiser tanks as they were known in the United Kingdom, were somewhat heavier and focused on long-range high-speed travel. Finally, the heavy or infantry tanks were heavily armoured and generally very slow. The overall idea was to use infantry tanks in close concert with infantry to effect a breakthrough, their heavy armour allowing them to survive enemy anti-tank weapons. Once this combined force broke the enemy lines, groups of cruiser tanks would be sent through the gap, operating far behind the lines to attack supply lines and command units. This one-two punch was the basic combat philosophy of the British tank formations, and was adopted by the Germans as a major component of the blitzkrieg concept. J.F.C. Fuller's doctrine of WWI was the fount for work by all the main pioneers: Hobart in Britain, Guderian in Germany, Chaffee in the U.S., de Gaulle in France, and Tukhachevsky in the USSR. All came to roughly the same conclusions, Tukhachevsky's integration of airborne pathfinders arguably the most sophisticated; only Germany would actually put the theory to practise, and it was their superior tactics, not superior weapons, that made blitzkrieg so formidable.

There was thought put into tank-against-tank combat, but the focus was on powerful anti-tank guns and similar weapons, including dedicated anti-tank vehicles. This achieved its fullest expression in the United States, where tanks were expected to avoid enemy armour, and let dedicated tank destroyer units deal with them. Britain took the same path, and both produced light tanks in the hope that with speed, they could avoid being hit, comparing tanks to ducks. In practice these concepts proved dangerous. As the numbers of tanks on the battlefield increased, the chance of meetings grew to the point where all tanks had to be effective anti-tank vehicles as well. However, tanks designed to cope only with other tanks were relatively helpless against other threats, and were not well suited for the infantry support role. Vulnerability to tank and anti-tank fire led to a rapid up-armouring and up-gunning of almost all tank designs. Tank shape, previously guided purely by considerations of obstacle clearance, now became a trade-off, with a low profile desirable for stealth and stability.

World War Two

World War II saw a series of advances in tank design. Germany, for example, initially fielded lightly armoured and armed tanks, such as the Panzer I, which had been intended for training use only. These fast-moving tanks and other armoured vehicles were a critical element of the Blitzkrieg. However, they fared poorly in direct combat with British tanks and suffered severely against the Soviet T-34, which was superior in armour, weaponry and cross-country performance while being equal in speed. By the end of the war all forces had dramatically increased their tanks' firepower and armour; for instance, the Panzer I had only two machine guns, and the Panzer IV, the "heaviest" early war German design, carried a low-velocity 75mm gun and weighed under twenty tonnes. By the end of the war the standard German medium tank, the Panther, mounted a powerful, high-velocity 75mm gun and weighed forty-five tonnes.

Another major wartime advance was the introduction of radically improved suspension systems. The quality of the suspension is the primary determinant of a tank's cross-country performance. Tanks with limited suspension travel subject their crew to massive shaking; this not only limits the speed at which the tank can travel, but also prevents firing while moving. Newer systems like the Christie or torsion bar suspension dramatically improved performance, allowing the late-war Panther to travel cross country at speeds that would have been difficult for earlier designs to reach on pavement.

By this time most tanks were equipped with radios (all U.S. and German, some Soviet; British radios were common, but often of indifferent quality), vastly improving the direction of units. Tank chassis were adapted to a wide range of military jobs, including mine-clearing and combat engineering tasks. All major combatant powers also developed specialised self-propelled guns: artillery, tank destroyers, and assault guns (armoured vehicles carrying large-calibre guns). German and Soviet assault guns, simpler and cheaper than tanks, had the heaviest guns in any vehicles of the war, while American and British tank destroyers were scarcely distinguishable (except in doctrine) from tanks.

Turrets, which were not previously a universal feature on tanks, were recognised as the most efficient siting of the main gun. In order to engage armoured targets the tank needed a single, powerful gun, unlike some prewar designs (like the Soviet T-35), which were often equipped with multiple turrets featuring low-calibre armament, or else mounted one larger gun in a fixed position. Most tanks retained at least one hull machine gun.

The Cold War and beyond

A Polish tank company equipped with T-54 tanks

After WWII, tank development proceeded largely as it had before, with improvement to both the medium and heavy classes. Light tanks were now limited to the reconnaissance role, and in U.S. use, airborne support as well. However, the weight limitations of air transport made a practical light tank almost impossible to build, and this class gradually disappeared over time.

But the seeds for a true transformation had already been working their way into existing designs. A combination of better suspensions and greatly improved engines allowed late-war medium tanks to outperform early-war heavies. With only slightly more armour and somewhat larger engines to compensate, mediums were suddenly protected against almost all anti-tank weapons, even those mounted on heavy tanks, while at the same time having the mobility of a medium tank. Many consider the turning point to be the Panther, which became the inspiration for almost every tank design after it. However, the Panther was not terribly well armoured, and could not really fight the heavy tanks on an equal basis.

A highly successful post-war tank was the Soviet T-54, which started production in 1947. This successor to the T-34 of World War II represented a direct evolution of that tank's design principles, improving on its low profile, good armour, high mobility, and adding a 100mm tank gun.

Another new tank was the British Centurion tank. Centurion marks built in the late 1950s were able to resist hits from the infamous German 88 mm gun, were armed with the deadly 105 mm Royal Ordnance L7, and could reach 56 km/h due to the excellent 650-hp Rolls-Royce Meteor engine. The Centurion replaced all British medium cruiser tanks and finally led to the demise of the heavy infantry tank class entirely, becoming what the British referred to as the Universal Tank, soon to be known as the main battle tank in most forces, abbreviated MBT.

In response to the threat of antitank guided missiles (ATGMs), the focus in development shifted away from armour thickness, to armour technology. Gun technology remained remarkably similar even to WWI-era gun technology, with most tanks in service still being manually loaded, but with big advances in shell effectiveness.

Although the basic roles and traits of tanks were almost all developed by the end of WWI, the performance of twenty-first-century counterparts had increased by an order of magnitude. They had been refined dramatically in response to continually changing threats and requirements, especially the threat of other tanks. The advancing capabilities of tanks have been balanced by developments of other tanks and by continuous development of anti-tank weapons.

Design

The three traditional factors determining a tank's effectiveness are its firepower, protection and mobility. Also significant is shock action, the psychological effect of a tank's imposing battlefield presence on enemy soldiers.

Firepower is the ability of a tank to identify, engage, and destroy a target. Protection is the tank's ability to resist being detected, engaged, and disabled or destroyed by enemy fire. Mobility includes tactical mobility over diverse terrain on the battlefield, as well as strategic mobility the ability of the tank to be transported by road, rail, sea, and perhaps by air, to the battlefield.

Tank design is traditionally held to be a compromise between these three factors—it is not considered possible to maximise all three. For example, increasing protection by adding armour will increase weight and therefore decrease manoeuvrability; increasing firepower by using a larger gun will decrease both manoeuvrability and protection (due to decreased armour at the front of the turret).

Firepower

A US Medium Tank M4A3E8 tank fires from a prepared position during the Korean war

The crew of a tank must be able to quickly identify, engage, and destroy many types of targets on the battlefield, while maintaining high mobility. To this end, they are equipped with sophisticated detection and fire-control equipment, a large gun capable of firing armour-piercing and high-explosive ammunition, and machine guns for defence against infantry, light vehicles, and aircraft.

The main weapon of any modern tank is a single large gun. Tank guns are among the largest-calibre weapons in use on land, with only a few artillery pieces being larger. Although the calibre has not changed substantially since the end of the Second World War, modern guns are technologically superior. The current common sizes are 120mm calibre for Western tanks and 125mm for Eastern (Soviet and Chinese legacy) tanks. Tank guns have been able to fire many types of rounds, but their current use is commonly limited to kinetic energy (KE) penetrators and high explosive (HE) rounds. Some tanks can fire missiles through the gun. Smoothbore (rather than rifled) guns are the dominant type of gun today. The British Army and the Indian Army are now the only ones to field main battle tanks carrying rifled guns.

Modern tank guns are generally fitted with thermal jackets which reduce the effect of uneven temperature on the barrel. For instance, if it were to rain on a tank barrel the top would cool faster than the bottom, or a breeze on the left might cause the left side to cool faster than the right. This uneven cooling will cause the barrel to bend slightly and will affect long range accuracy.

Usually, tanks carry other armament for short range defence against infantry or targets where the use of the main weapon would be ineffective or wasteful. Typically, this is a small calibre (7.62 to 12.7 mm) machine gun mounted coaxially with the main gun. However, a couple of French tanks such as the AMX-30 and AMX-40 carry a coaxial 20mm cannon that has a high rate of fire and can destroy lightly armoured vehicles. Additionally, many tanks carry a roof-mounted or commander's cupola machine gun for close-in ground or limited air defence. The 12.7-mm and 14.5-mm machine guns commonly carried on U.S. and Russian tanks and the French Leclerc are also capable of destroying lightly-armoured vehicles at close range.

Some tanks have been adapted to specialised roles and have had unusual main armament such as flame-throwers. These specialised weapons are now usually mounted on the chassis of an armoured personnel carrier.

Fire control

Historically, tank weapons were aimed through simple optical sights and laid onto target by hand, with windage estimated or assisted with a reticle. Range to the target was estimated with the aid of a reticle (markings in the gun sight which are aligned to frame an object of known size, in this case a tank). Consequently, accuracy was limited at long range and concurrent movement and accurate shooting were largely impossible. Over time these sights were replaced with stereoscopic range-finders, and later by Laser range-finders.

Most modern main battle tanks in the armies of industrialised countries use laser range-finders but optical and reticule range-finders are still in use in older and less sophisticated vehicles. Modern tanks have a variety of sophisticated systems to make them more accurate. Gyroscopes are used to stabilise the main weapon; computers calculate the appropriate elevation and aim-point, taking input from sensors for wind speed, air temperature, humidity, the gun-barrel temperature, warping and wear, the speed of the target (calculated by taking at least two sightings of the target with the range-finder), and the movement of the tank. Infrared, light-amplification, or thermal night vision equipment is also commonly incorporated. Laser target designators may also be used to illuminate targets for guided munitions. As a result modern tanks can fire reasonably accurately while moving.

Ammunition

There are several types of ammunition designed to defeat armour, including High explosive squash head (HESH, also called high explosive plastic, HEP), High explosive anti-tank (HEAT), and kinetic energy penetrators (KEP, or armour-piercing discarding sabot APDS). For accuracy, shells are spun by gun-barrel rifling, or fin-stabilised (APFSDS, HEAT-FS, etc.).

Some tanks, including the M551 Sheridan, T-72, T-64, T-80, T-90, T-84, and PT-91 can fire ATGMs (anti-tank guided missile) through their gun barrel or from externally mounted launchers. This functionality can extend the effective combat range of the tank beyond the range afforded by conventional shells, depending on the capabilities of the ATGM system. It also provides the tank with a useful weapon against slow, low-flying airborne targets like helicopters. The United States has abandoned this concept, phasing the M551 and M60A2 out of their forces in favour of helicopters and aircraft for long range anti-tank roles, but CIS countries continue to employ gun-missile systems in their main battle tanks.

Protection

Sections of the side-skirt are swung aside on this M1 Abrams tank to expose the track so that a road wheel can be replaced. Photo from B Company, 4th Tank Battalion, 4th Marine Division, US Marines.

An M1 Abrams tank on lookout. Heat haze from the turbine engine can be seen to the rear.

A tank's protection is the combination of its ability to avoid detection, to avoid being hit by enemy fire, the ability of its armour to resist the effects of enemy fire, and its ability to sustain damage and complete its mission, or at least protect its crew.

Avoiding detection

Stationary tanks can be well camouflaged in woodland and forested areas where there is natural cover, making detection and attack from the air more difficult. By contrast, in the open it is very hard to hide a tank. In both cases, however, once a tank starts its engine or begins to move it can be detected much more easily due to the heat and noise generated by its engine. The tank tracks across lands can be spotted from the air, and in the desert movement can stir up dust clouds several times the size of the tanks.

A recently stopped stationary tank has a considerable heat signature. Indeed even if the tank itself is hidden, for example behind a hill, it is still possible for a skilled operator to detect the tank from the column of warmer air above the tank. This risk can be reduced somewhat by the use of thermal blankets which reduce the radiation of heat while the engine and tracks cool. Some camouflage nets are manufactured from unevenly distributed mix of materials with differing thermal properties, which are designed to "randomise" or at least reduce the regularity of the thermal signature of a tank.

Tanks are powered by a diesel or turbine engine of a power comparable to a diesel locomotive. From the outside a diesel powered tank smells, sounds, and feels quite like a diesel locomotive. The deep rumble of even a single tank can be heard a great distance on a quiet day, and the sharp diesel smell can be carried far downwind. When a tank stands still with engine running the land trembles around it. When moving, the vibrations are greater. The acoustic and seismic signatures of multi-fuel engines are comparable. The acoustic signature of a turbine engine is much greater: its high-pitched whine can be much more easily distinguished from other sounds, near or far.

The very large power output of modern tank engines (typically in excess of 750 kW or 1,000 hp) ensure that they produce a distinct thermal signature. The unusually compact mass of metal of the tank hull dissipates heat in a fashion which marks it off sharply from other objects in the countryside. A moving tank is thus relatively easy to spot by good land-based or aerial infrared scanners. One of the reasons for the one-sided fighting during the Gulf War was that tanks like M1 Abrams had almost four times the night-time infrared scanning range of T-72s used by the Iraqi army. Another factor in the Gulf War was that, even when camouflaged and not moving, Iraqi tanks at night would cool at a different rate from their surroundings, making thermal detection easier.

Getting a tank to move proved to be important in the Kosovo conflict in 1999. During the initial few weeks of the conflict NATO air sorties were rather ineffective in destroying Serbian tanks. This changed in the final week of the conflict, when the Kosovo Liberation Army began to engage tanks. Although the KLA had little chance of destroying the tanks, their purpose was to get the tanks to move whereupon they could be more easily identified and destroyed by NATO air power.

Armour

Abandoning a disabled M-3 tank in training

The main battle tank is the most heavily armoured vehicle in modern armies. Its armour is designed to protect the vehicle and crew against a wide variety of threats. Commonly, protection against kinetic energy penetrators fired by other tanks is considered the most important. Tanks are also vulnerable to antitank guided missiles; antitank mines, larger bombs, and direct artillery hits, which can disable or destroy them. Tanks are especially vulnerable to airborne threats. Most modern MBTs do offer near complete protection from artillery fragmentation and lighter antitank weapons such as rocket propelled grenades. The amount of armour needed to protect against all conceivable threats from all angles would be far too heavy to be practical, so when designing an MBT much effort goes into finding the right balance between protection and weight.

Most armoured fighting vehicles are manufactured of hardened steel plate, or in some cases aluminium. The relative effectiveness of armour is expressed by comparison to rolled homogeneous armour.

Most armoured vehicles are best-protected at the front, and their crews always try to keep them pointed toward the likeliest direction of the enemy. The thickest and best-sloped armour is on the glacis plate and the turret front. The sides have less armour and the rear, belly and roof are least protected. Today, tanks are vulnerable to specialised top-attack missile weapons and air attack. During World War II, aircraft rockets earned a formidable reputation, especially in France after the Normandy landings ( Operation Neptune); post-war analysis revealed many reported kills were near-misses. Aircraft cannon firing armour-piercing ammunition, such as the Hurribomber's 40mm or Stuka's 37mm, could be effective, also. Even a simple Molotov cocktail on the engine deck, however, may disable most tanks.

Before the Second World War, several tank designers tried sloping the armour on experimental tanks. The most famous and successful example of this approach at the time was the T-34. Angling armour plates greatly increases their effectiveness against projectiles, by increasing the effective perpendicular thickness of the armour, and by increasing the chance of deflection. German tank crews were said to be horrified to find that shots fired at the angled plates of T-34s would sometimes simply ricochet.

Even light infantry antitank weapons can immobilise a tank by damaging its suspension or track. Many tracked military vehicles have side skirts, protecting the suspension.

High explosive anti-tank weapons (HEAT), such as the bazooka, were a new threat in the Second World War. These weapons carry a warhead with a shaped charge, which focuses the force of an explosion into a narrow penetrating stream. Thin plates of spaced armour, steel mesh " RPG screens", or rubber skirts, were found to cause HEAT rounds to detonate too far from the main armour, greatly reducing their penetrating power.

British Challenger 2 tank, fitted with Chobham Armour.

Some anti-tank ammunition (HESH or HEP) uses flexible explosive material, which squashes against a vehicle's armour, and causes dangerous spalling of material inside the tank when the charge explodes. This may kill the crew without penetrating the armour, still neutralising the tank. As a defence, some vehicles have a layer of anti-spall material lining their insides.

Since the 1970s, some tanks have been protected by more complex composite armour, a sandwich of various alloys and ceramics. One of the best types of passive armour is the British-developed Chobham armour, which is comprised of spaced ceramic blocks contained by a resin- fabric matrix between layers of conventional armour. A form of Chobham armour is encased in depleted uranium on the very well-protected M1A1 Abrams MBT.

The Israeli Merkava tank takes the design of protection systems to an extreme, using the engine and fuel tanks as secondary armour.

When the armour is defeated then the ability of the surviving crew to escape becomes an issue. The provision of escape hatches in for instance the bottom of the hull as in the T-34 or the side, as in the Churchill, are necessary potential weaknesses in the armour.

Passive defences

Most armoured vehicles carry smoke grenade launchers which can rapidly deploy a smoke screen to visually shield a withdrawal from an enemy ambush or attack. The smoke screen is very rarely used offensively, since attacking through it blocks the attacker's vision and gives the enemy an early indication of impending attack. Modern smoke grenades work in the infrared as well as visible spectrum of light.

Some smoke grenades are designed to make a very dense cloud capable of blocking the laser beams of enemy target designators or range finders and of course obscuring vision, reducing probability of a hit from visually aimed weapons, especially low speed weapons, such as anti-tank missiles which require the operator to keep the tank in sight for a relatively long period of time. In many MBTs, such as the French-built Leclerc, the smoke grenade launchers are also meant to launch tear gas grenades and anti-personnel fragmentation grenades. Many Israeli tanks contain small vertical mortar tubes which can be operated from within the tank, enhancing the anti-personnel capabilities and allowing it to engage targets which are behind obstacles. There have been proposals to equip other tanks with dual-purpose smoke/fragmentation grenade launchers that can be reloaded from the interior.

Prior to the widespread introduction of thermal imaging the most common smoke grenade in AFV launchers was white phosphorus which created a very rapid smoke screen as well as having a very useful incendiary effect against any infantry in the burst area (e.g., infantry attempting to close with hand placed charges or mines).

Since the advent of thermal imagers most tanks carry a smoke grenade that contains a plastic or rubber compound whose tiny burning fragments provide better obscurant qualities against thermal imagers.

Some tanks also have smoke generators which can generate smoke continuously, rather than the instantaneous, but short duration of smoke grenades. Generally smoke generators work by injecting fuel into the exhaust, which partially burns the fuel, but leaves sufficient unburned or partially burned particles to create a dense smoke screen.

Modern tanks are increasingly being fitted with passive defensive systems such as laser warning devices, which activate an alarm if the tank is "painted" by a laser range-finder or designator.

Other passive defences include radio warning devices, which provide warning if the tank is targeted by radar systems that are commonly used to guide antitank weapons such as millimetre and other very short wave radar.

Countermeasures

Explosive reactive armour, or ERA, is another major type of protection against high explosive antitank weapons, in which sections of armour explode to dissipate the focused explosive force of a shaped charge warhead. Reactive armour is attached to the outside of an MBT in small, replaceable bricks.

Active protection systems go one step further than reactive armour. An APS uses radar or other sensing technology to automatically react to incoming projectiles. When the system detects hostile fire, it calculates a firing resolution and directs an explosive-launched counter-projectile to intercept or disrupt the incoming fire a few metres from the target.

Exposed crew

An Australian Sentinel tank during trials in 1942. Note the commander's lack of protection.

Paradoxically, a tank is usually in its safest state when the commander is in a personally unsafe position, riding in the open, head out of the turret. In this rather high position, with no personal protection save maybe a helmet and a flak jacket, the commander can see around the vehicle with no restrictions, and has the greatest chance of spotting enemy antitank operations or natural and artificial obstacles which might immobilise or slow down the tank. Also, the tank itself is less visible as it can stay lower behind obstacles.

Tank periscopes and other viewing devices give a sharply inferior field of vision and sense of the countryside. Thus, when a tank advances in hostile territory with hatches closed, the commander and the crew might be personally safer, but the tank as a whole is more at risk given the extremely reduced vision. In order to overcome this problem improvements in onboard optical systems are ongoing.

Mobility

There are essentially three main aspects of mobility to consider, the tank's basic mobility such as its speed across terrain, the ability to climb obstacles and its overall battlefield mobility such as range, what bridges it can cross, and what transport vehicles can move it and turning. Mobility is what tankers and tank designers call 'agility'. Mobility of a tank is categorised as Battlefield Mobility, Tactical Mobility, or Strategic Mobility. The first is a function of its engine performance and capability of its running gear and is determined by aspects such as acceleration, speed, vertical obstacle capability and so on. The second is the ability of the tank to be readily transported within a theatre of operation. The third is its ability to be transported from one theatre of operation to other, dependent on its weight, air portability and so on.

A main battle tank is designed to be very mobile and able to tackle most types of terrain. Its wide tracks disperse the heavy weight of the vehicle over a large area, resulting in a specific ground pressure that might be lower than that of a man's foot . The types of terrain that do pose a problem are usually extremely soft ground such as swamps, or rocky terrain scattered with large boulders. In "normal" terrain, a tank can be expected to travel at about 30 to 50 km/h. The road speed may be up to 70 km/h.

The logistics of getting from point A to point B are not as simple as they appear. On paper, or during any test drive of a few hours, a single tank offers better off-road performance than any wheeled fighting vehicle. On the road the fastest tank design is not much slower than the average wheeled fighting vehicle design. But in practice, the huge weight of the tank combined with the relative weakness of the track assembly makes the maximum road speed of a tank really a burst speed, which can be kept up for only a short time before there is a mechanical breakdown. Although the maximum off-road speed is lower, it cannot be kept up continuously for a day, given the variety and unpredictability of off-road terrain (with the possible exception of plains and sandy deserts).

A Leclerc crossing a gap.

Since an immobilised tank is an easy target for mortars, artillery, and the specialised tank hunting units of the enemy forces, speed is normally kept to a minimum, and every opportunity is used to move tanks on wheeled tank transporters and by railway instead of under their own power. Tanks invariably end up on railcars in any country with a rail infrastructure, because no army has enough wheeled transporters to carry all its tanks. Planning for railcar loading and unloading is crucial staff work, and railway bridges and yards are prime targets for enemy forces wishing to slow a tank advance.

When moving in a country or region with no rail infrastructure and few good roads, or a place with roads riddled by mines or frequent ambushes, the average speed of advance of a tank unit in a day is comparable to that of a man on a horse or bicycle. Frequent halts must be planned for preventive maintenance and verifications in order to avoid breakdowns during combat. This is in addition to the tactical halts needed so that the infantry or the air units can scout ahead for the presence of enemy antitank groups.

Another mobility issue is getting the tank to the theatre of operations. Tanks, especially main battle tanks, are extremely heavy, making it very difficult to airlift them. Using sea and ground transportation is slow, making tanks problematic for rapid reaction forces.

Some tank-like vehicles use wheels instead of tracks in order to increase road speed and decrease maintenance needs. These vehicles lack the superior off-road mobility of tracked vehicles, but are considered by United States planners as more suited for rapid reaction forces due to increased strategic mobility .

Water operations

For most tanks water operations are limited to fording. The fording depth is usually limited by the height of the air intake of the engine, and to a lesser extent the driver's position. The typical fording depth for MBTs is 90 to 120 cm. (3-4 Feet.)

Deep fording

A T-90, snorkel erected.

However, with preparation some tanks are able to ford considerably deeper waters. The West German Leopard I and Leopard II tanks can ford to a depth of several metres, when properly prepared and equipped with a snorkel. The Leopard snorkel is in fact a series of rings which can be stacked to create a long tube. This tube is then fitted to the crew commander's hatch and provides air and a possible escape route for the crew. The height of the tube is limited to around three meters.

Some Russian/Soviet tanks are also able to perform deep fording operations, however unlike the Leopard, the Russian snorkel is only a few inches round and does not provide a crew escape path. Russian snorkels are also fixed in length, providing only a couple of metres of depth over the turret height.

This type of fording requires careful preparation of the tank and the ingress and egress sites on the banks of the water obstacle. Tank crews usually have a negative reaction towards deep fording. This has influenced tactics in those countries where the psychological health of the crews or their capacity for rebellion is taken into account. However, if properly planned and executed this type of operation adds considerable scope for surprise and flexibility in water crossing operations.

Amphibious tanks

Sherman DD (Duplex Drive) amphibious tank with waterproof float screens, in 1944. The float screen was raised in the water and rear propellers provided forward thrust.

Some light tanks such as the PT-76 are amphibious, typically being propelled in the water by hydrojets or by their tracks.

Often a fold down trim vane is erected to stop water washing over the bow of the tank and thus reducing the risk of the vehicle being swamped via the driver's hatch.

In World War II the M4 Medium Tank "Sherman" was made amphibious with the addition of a rubberised canvas screen to provide additional buoyancy. It was propelled by propellers driven by the main engine. This was referred to as the Sherman DD (Duplex Drive) and was used on D-Day to provide close fire support on the beaches during the initial landings. The Sherman DD could not fire when afloat as the buoyancy screen was higher than the gun. A number of these DDs swamped and sank in the operation. This was due to rough weather in the English Channel (with some tanks having been launched too far out), and due to turning in the current to converge on a specific point on the battlefield, which allowed waves to breach over the screens. Those that did make it ashore, however, provided essential fire support in the first critical hours.

Power plants

The tank's power-plant supplies power for moving the tank and for other tank systems, such as rotating the turret or electrical power for a radio. Tanks fielded in WWI mostly used petrol (gasoline) engines as power-plants, unlike the American Holt Gas-Electric tank which was powered by a petrol (gasoline) engine and an electric engine. In the Second World War there was a mix of power-plant types used; a lot of tank engines were adapted aircraft engines. As the Cold War started, tanks had almost all switched over to using diesel, improved multi-fuel versions of which are still common. Starting in the late 1970s, turbine engines began to appear.

The weight and type of power-plant (influenced by its transmission and drive train) largely determines how fast and mobile the tank is, but the terrain effectively limits the maximum speed of all tanks through the stress it puts on the suspension and the crew.

Multi-fuel diesels

All modern non-turbine tanks use a diesel engine because diesel fuel is less flammable and more economical than petrol. Some Soviet tanks used the dark smoke of burning diesel as an advantage and could intentionally burn fuel in the exhaust to create smoke for cover. Fuel tanks are commonly placed at the rear of the tank, though in some designs, such as the Israeli Merkava, the diesel fuel tanks are placed around the crew area to provide an additional layer of "armour." Fuel has often been stored in auxiliary tanks externally, or by other means such as in a small trailer towed behind the tank, able to be detached during combat.

Modern tank engines are in some cases multi-fuel engines, which can operate on diesel, petrol or similar fuels.

Gas turbines

Gas turbine engines have been used as an auxiliary power unit (APU) in some tanks, and are the main power plant in the Soviet/Russian T-80 and U.S. M1 Abrams. They are comparatively lighter and smaller than diesel engines; at the same level of sustained power output (the T-80 was dubbed the Flying Tank for its high speed).

However they are much less fuel efficient, especially at low RPMs, requiring larger fuel tanks to achieve the same combat range. Different models of the M1 Abrams have addressed this problem with battery packs or secondary generators to power the tank's systems while stationary, saving fuel by reducing the need to idle the main turbine. T-80 tanks are commonly seen with large external fuel tanks to extend their range. Russia has replaced T-80 production with the less powerful T-90 (based on the T-72), while Ukraine has developed the diesel-powered T-80UD and T-84 with nearly the power of the gas-turbine tank.

Because of their lower efficiency, the thermal signature of a gas turbine is higher than a diesel engine at the same level of power output. On the other hand the acoustic signature of a tank with a muffled gas turbine can be quieter than a piston engine–powered one. The M1A2 was nicknamed Whispering Death for its quiet operation.

A turbine is theoretically more reliable and easier to maintain than a piston-based engine, since it has a simpler construction with fewer moving parts. In practice, however, those parts experience a higher wear due to their higher working speeds. The turbine blades are also very sensitive to dust and fine sand, so that in desert operations special filters have to be carefully fitted and changed several times daily. An improperly fitted filter, or a single bullet or piece of shrapnel can render the filter useless, potentially damaging the engine. Piston engines also need well-maintained filters, but they are more resilient if the filter does fail.

Like most modern diesel engines used in tanks, gas turbines are usually multi-fuel engines.

Command, control and communications

Commanding and coordinating a tank organisation in the field has always been subject to particular problems. Because of the isolation of small units, individual vehicles, and even the crewmen of a tank, special arrangements have had to be made. Armoured bulkheads, engine noise, intervening terrain, dust, and smoke, and the need to operate "hatches down" (or "buttoned up") comprise severe detriments to communications.

Internal communications

Every action of a tank's crew, movement and fire, is ordered by its commander. In some early tanks, the crew commander's task was severely hampered by having to load or fire the main armament, or both. In many small armoured fighting vehicles, even into the late twentieth century, the crew commander would relay movement orders to the driver by kicks to his shoulders and back. Most modern AFVs are equipped with an intercom, allowing all crew members to talk to each other, and to operate the radio equipment. Some tanks have even been equipped with an external intercom on the rear, to allow co-operating infantry to talk to the crew.

Tactical communications

In the earliest tank operations, communications between the members of an armoured company were accomplished using hand signals or handheld semaphore flags, and in some situations, by crew members dismounting and walking to another tank. In World War One, situation reports were sent back to headquarters by releasing carrier pigeons through vision slits. Signal flares, smoke, movement, and weapons fire are all used by experienced crews to coordinate their tactics.

From the 1930s to the '50s, most nations' armoured forces became equipped with radios, but visual signals are still used to reduce radio chatter. A modern tank is usually equipped with radio equipment allowing its crew to communicate on a company or battalion radio network, and possibly to monitor a higher-level network, to coordinate with other arms of service. Company or battalion commanders' tanks usually have an additional radio. Communications on a busy network are subject to a set of formalised language rules called radio voice procedure.

Most armoured forces operate with the crew commander, and possibly other crew members, "hatches up", for best possible situational awareness. When taking fire, or in potential NBC conditions, tank crews "button up" and only view the battlefield through vision slits or periscopes, severely reducing their ability to acquire targets and perceive hazards. Since the 1960s, a tank's commander has had progressively more sophisticated equipment for target acquisition. In a main battle tank, the commander has his own panoramic sights (with night-vision equipment), allowing him to designate one or more new targets, while the gunner engages another. More advanced systems allow the commander to take control of the turret and fire the main armament in an emergency.

Computerised advances

A recent development in AFV equipment is the increased integration of fire control, the laser range-finder, GPS data, and digital communications. U.S. tanks are fitted with digital computers which are connected into battlefield networks. These integrate known information on enemy targets and friendly units to greatly improve the tank commander's situational awareness. In addition to easing the reporting burden, these systems also allow for orders to be given complete with graphics and overlays, via the network.

See also:

Military communications

Command, control, and communications (C3I)

C4ISTAR

Vulnerability

Despite being a powerful weapon and an impressive sight on the battlefield, the tank is vulnerable. In fact, the tank's effectiveness has led to massive development of antitank weapons.

Infantry

Despite a tank's long-range firepower and shock action against inexperienced infantry, unsupported tanks are vulnerable to attacks by foot soldiers when attacking defensive positions, in close terrain, and in built up areas. Tank weapons have blind spots below their minimum depression, and a tank's suspension and relatively thin rear and top armour are vulnerable to attacks from nearby and from the upper storeys of buildings.

Tanks generally operate with closely coordinated infantry support to protect them from enemy infantry.

Artillery

Since World War II, tanks are sufficiently armoured to protect against artillery shell fragments. Only massive barrages are likely to destroy tanks with lucky direct hits, or flip them over by near-misses with very heavy high-explosive shells. Artillery guns usually also have a few rounds of antitank ammunition for defence against tanks in direct fire.

Since the 1970s, there have been several types of artillery ammunition developed which can attack armoured vehicles. These include guided projectiles which home in on a target painted by a laser designator. There are also cluster munitions, saturating an area with bomblets which can attack top armour or create a minefield, and even smart submunitions which can identify and attack nearby tanks.

Mines

Antitank minefields are area-denial weapons, helping to defend an area which is covered by fire, or channel enemy movements to prepared kill zones. Undefended minefields or individual mines planted in roadways are also used to delay movement and act as a nuisance weapon, but are not considered a highly effective military weapon—although their effect on morale and public support for military missions is used by insurgents.

Land mines attack a vehicle's relatively fragile suspension and thinner bottom armour, and many armoured vehicles are designed to reduce their effect. There are also off-route mines, which use a shaped-charge HEAT warhead to attack from the side. Guerilla fighters who don't have antitank mines at their disposal may build improvised explosive devices for harassment of armoured forces.

Aircraft

Starting in the Second World War, ground attack aircraft have been able to destroy tanks using heavy machine guns, cannon, rockets, and guided missiles or guided bombs.

Since the 1960s, another threat is the attack helicopter, exploiting high mobility and the use of terrain for protection, and carrying sophisticated fire-control equipment and heavy guided missiles. A helicopter is able to make a pop-up attack from behind cover, only exposing itself briefly.

Logistics

Tanks have very high logistical requirements. They are very hungry for fuel, ammunition, maintenance, and replacement parts. Armoured forces cannot fight effectively if their requirements cannot be met due to shortages, poor planning, or enemy actions.

They can also be disabled by the weather: starter batteries and lubricants fail in extreme cold, while engines and crew-members overheat in very hot weather.

Future research and development

There has been much speculation as to how tanks will evolve for modern day conflicts. Current research involves making the tank invisible to radar by adapting stealth technologies originally designed for aircraft and a variety of luminosity and colour shaping technologies. Research is also ongoing in armour systems and new propulsion units.

One clear trend is the increasing number of electrical and communication systems on a tank, such as thermal scopes and higher powered radios.

If tank designs switched to electrical motors like some other heavy construction equipment, rather than a direct drive transmission, or used electromagnetic guns, as is being studied for ships, there would still be a need for a good power-plant. The turbine engine and diesel (or multi-fuel) power plants meet current power needs but it is also possible that other types of power-plants such as fuel cells will provide a viable option, and they have been experimented with. For example, a hybrid electric version of the M113 APC outperformed the conventional one in many areas, but only at the expense of smaller range. Reduction of signatures and multi-fuel capability give the Stirling engine an advantage, and it has been examined.

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